Update index.rst with whats new for 2.8 #5026

Job	Run time
pytorch_tutorial_build_worker (6, 15, linux.g5.4xlarge.nvidia.gpu)	27m 34s
pytorch_tutorial_build_worker (5, 15, linux.g5.4xlarge.nvidia.gpu)	22m 48s
pytorch_tutorial_build_worker (2, 15, linux.g5.4xlarge.nvidia.gpu)	24m 40s
pytorch_tutorial_build_worker (7, 15, linux.g5.4xlarge.nvidia.gpu)	26m 18s
pytorch_tutorial_build_worker (3, 15, linux.g5.4xlarge.nvidia.gpu)	23m 28s
pytorch_tutorial_build_worker (4, 15, linux.g5.4xlarge.nvidia.gpu)	34m 43s
pytorch_tutorial_build_worker (1, 15, linux.g5.12xlarge.nvidia.gpu)	15m 7s
pytorch_tutorial_build_worker (13, 15, linux.g5.4xlarge.nvidia.gpu)	14m 56s
pytorch_tutorial_build_worker (12, 15, linux.g5.4xlarge.nvidia.gpu)	15m 53s
pytorch_tutorial_build_worker (9, 15, linux.g5.4xlarge.nvidia.gpu)	20m 17s
pytorch_tutorial_build_worker (14, 15, linux.g5.4xlarge.nvidia.gpu)	29m 36s
pytorch_tutorial_build_worker (11, 15, linux.g5.4xlarge.nvidia.gpu)	13m 46s
pytorch_tutorial_build_worker (10, 15, linux.g5.4xlarge.nvidia.gpu)	30m 39s
pytorch_tutorial_build_worker (15, 15, linux.g5.4xlarge.nvidia.gpu)	19m 42s
pytorch_tutorial_build_worker (8, 15, linux.g5.4xlarge.nvidia.gpu)	24m 39s
pytorch_tutorial_build_manager	21m 3s
	6h 5m 9s

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